Problem: mos farm stand sold a total of 165 pounds of apple's and peaches. she sold apple's for $1.75 per pound and peaches for $2.50 per pound. if she made $337.50, how many pounds of peaches did she sell?

Let x be pounds of apples, and y be pounds of peaches.
x+y= 165 ... total of pounds sold
1.75x+2.50y= 337.5   total of money earned
Solve this system:
x=165-y
1.75(165-y)+2.50y=337.5
288.75-1.75y+2.50y=337.5
0.75y=337.5-288.75
0.75y=48.75
y=48.75/0.75
y= 65
She sold 65 pounds of peaches

Yes, two vertical lines can be complementary